Tetrahedron
Letters
Tetrahedron Letters 47 (2006) 335–339
Enantiospecific first total synthesis of (+)-2b-hydroxysolanascone,
the aglycone of the phytoalexin isolated from flue-cured
tobacco leaves
A. Srikrishna* and S. S. V. Ramasastry
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560012, India
Received 20 September 2005; revised 27 October 2005; accepted 3 November 2005
Available online 18 November 2005
Abstract—The first total synthesis of (+)-2b-hydroxysolanascone, the aglycone of the phytoalexin 2b-hydroxysolanascone-b-glucopyranoside isolated from flue-cured tobacco leaves (N. tabacum L., OCL), and its 2,10-diepi- and 2a-epimers has been accomplished,
starting from the readily available monoterpene (R)-carvone.
Ó 2005 Elsevier Ltd. All rights reserved.
Phytoalexins are antibacterial, fungicidal, low molecular
weight secondary metabolites produced as a means of
self-defense in plants. The isolation of the structurally
complex tetracyclic phytoalexin solanascone 1 was first
reported by Fujimori and co-workers in 1978, from
Nicotiana tabacum cv. Burley.1,2 In 1983, the research
group of Nishikawaji reported the isolation of dehydrosolanascone 2 from flue-cured tobacco leaves.3 An
oxygenated derivative, 9-hydroxysolanascone-b-sophoroside 3 was later isolated from flue-cured tobacco
leaves by Kodama et al.4 In 1986, Tazaki and
co-workers reported two more solanascane derivatives,
13-hydroxysolanascone-b-glucopyranoside 4 and 15hydroxysolanascone-b-glucopyranoside 5 from fluecured tobacco.5 Subsequently, they also reported the
isolation of 2b-hydroxysolanascone-b-glucopyranoside
6 and 3b-hydroxysolanascone-b-glucopyranoside 7 from
flue-cured tobacco leaves (N. tabacum L., OCL).6 The
strong antibacterial activity of solanascones on Pseudomonas solanacearum has been well established.7
The unusual and novel tetracyclo[5.3.1.11,4.05,11]dodecane carbon framework2 incorporating three contiguous
quaternary carbon atoms and seven chiral centres, coupled with the biological activities made solanascanes
interesting and challenging synthetic targets.8 Recently,
we reported8 the enantiospecific total synthesis of solanascone 1 and dehydrosolanascone 2. In continuation,
* Corresponding author. Tel.: +91 80 22932215; fax: +91 80
23600529; e-mail: ask@orgchem.iisc.ernet.in
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.11.014
O
9
OGlc
O
O
12
11
H
1
H
H
6
3
1
2
R
13
3
O
O
H
15
R'
4 R = OGlc, R' = H
5 R = H, R' = OGlc
R
R'
H
6 R = OGlc, R' = H
7 R = H, R' = OGlc
8 R = OH, R' = H
herein, we report the enantiospecific first total synthesis
of 2b-hydroxysolanascone 8, the aglycone of the glycoside 6, starting from the monoterpene (R)-carvone 9.
A retrosynthetic analysis of 2-hydroxysolanascone 8 is
depicted in Scheme 1. Enone 10 was identified as the
key intermediate, which could be elaborated into 2hydroxysolanascones. For the enone 10, the diketone
11 was considered as an appropriate precursor, whose
synthesis from carvone 9 via 3-butenylcarvone 12 has
already been developed.8
The synthetic sequence (Schemes 2 and 3) was initiated
with the preparation of the diketone 11 as described earlier.8 Thus, a Barbier reaction between carvone 9 and 4bromobut-1-ene, followed by oxidation of the resultant
allylic tertiary alcohol furnished the 1,3-transposed
336
A. Srikrishna, S. S. V. Ramasastry / Tetrahedron Letters 47 (2006) 335–339
O
O
OPG
O
HO
O
O
8
9
11
10 (PG = protecting group)
Scheme 1.
O
O
a
O
O
O
b
c
O
d
O
O
9
12
13
11
O
14
e
OCOPh
OCOPh
O
O
g
h
18
i
OCOPh
19
f
O
O
O
17
16
j
O
15
O
PhOCO
O
OH
OCOPh
O
H
k
RO
21 R = COPh
22 R = H
l
20
Scheme 2. Reagents, conditions and yields: (a) (i) Li, BrCH2CH2CH@CH2, THF, ))), 1 h; (ii) PCC, silica gel, CH2Cl2, rt, 4 h, 85%; (b) 30% H2O2,
6 N aq NaOH, MeOH, 0 °C, 20 h, 85%; (c) Amberlyst-15 (1:1 w/w), CH2Cl2 (0.1 M), rt, 24 h, 74%; (d) (CH2OH)2, PTSA, C6H6, reflux, 45 min, 68%;
(e) LAH, Et2O, 0 °C ! rt, 1 h, 100%; (f) (i) C6H5COCl, py, DMAP, CH2Cl2, rt, 8 h; (ii) 3 N HCl, THF, 2 h; 91%; (g) PdCl2, CuCl, DMF–H2O (4:1),
O2, rt, 20 h, 82%; (h) piperidine, AcOH, C6H6, reflux, 45 min, 85%; (i) LHMDS, PhSeSePh, THF, 3.5 h, 70 °C; 30% H2O2, 30 min, 87%; (j)
Me2CuLi, Et2O, 30 °C, 1 h, 76%; (k) hm, MeOH, 1 h, 84%; (l) K2CO3, MeOH, 50 °C, 4 h, 86%.
enone (S)-3-(but-3-enyl)carvone 12.9 Epoxidation of the
enone 12 with 30% aqueous hydrogen peroxide in the
presence of sodium hydroxide furnished the anti-epoxide
13, in 85% yield, which on rearrangement with Amberlyst-15 generated the dione 11.10 Next, attention was
focused on the protection of the cyclopentanone ketone
in the dione 11. Thus, refluxing a benzene solution of the
diketone 11 with ethylene glycol in the presence of a catalytic amount of p-toluenesulfonic acid (PTSA) using a
Dean–Stark water trap furnished the keto-ketal 14 in
68% yield, in a highly regioselective manner, which on
reaction with LAH in ether at ice temperature furnished,
stereoselectively, the alcohol 15 in quantitative yield.
Reaction of the alcohol 15 with benzoyl chloride in pyridine in the presence of a catalytic amount of 4-N,Ndimethylaminopyridine (DMAP) at room temperature,
followed by hydrolysis of the ketal with 3 N aqueous
hydrochloric acid furnished the keto-benzoate 16 in
91% yield.
Treatment of the keto-benzoate 16 with 0.1 equiv of palladium chloride and 5 equiv of cuprous chloride in
DMF and water under an oxygen atmosphere (balloon)11 for 12 h produced, regioselectively, the diketobenzoate 17 in 82% yield. An intramolecular aldol
condensation of the diketobenzoate 17 with piperidine
and acetic acid in dry benzene using a Dean–Stark water
trap furnished the enone 18, in 85% yield, in a highly
regioselective manner. A two-step protocol was conceived for introducing the secondary methyl group at
the C-10 position via the cross-conjugated cyclohexadienone 19. Accordingly, reaction of the enone 18 with
lithium hexamethyldisilazide (LHMDS) and then diphenyl diselenide at 70 °C, followed by oxidation with
30% aqueous hydrogen peroxide at ice-bath temperature
generated the dienone 19 in 87% yield. Conjugate addition of lithium dimethylcuprate to the dienone 19 at
30 °C furnished the enone 20, in 76% yield, in a highly
regio- and stereoselective manner. Even though the stereochemistry of the C-10 methyl group was not established at this stage, since only one isomer is produced
in the reaction, it was tentatively assigned as anti to
the benzoate bearing carbon. It was surprising to note
that only one stereoisomer was formed in the cuprate
reaction8 even though the two substituents on the cyclopentane ring are anti to the C-10 carbon atom. One possible explanation for the observed stereoselectivity is the
p-stacking of the dienone system with the aromatic ring
of the benzoate blocking one side of the dienone in 19.
Photochemical irradiation of the enone 20 with a
450 W Hanovia medium pressure mercury vapor lamp
furnished the keto-benzoate 21 in a highly regioselective
and stereospecific manner, in 84% yield. Hydrolysis of
the benzoate group in 21 furnished 2a-hydroxy-10-epi-
A. Srikrishna, S. S. V. Ramasastry / Tetrahedron Letters 47 (2006) 335–339
O
O–
O
O
O
11
O
a
O
O
O
X Y
O
O
O
c
O
O
25
O
d
O
O
O
OCOPh
f
O
O
O
O
O
29
28
O
PhOCO
g
O
h
OCOPh
O
j
H
O
i
32
33
O
n
8
O
Ph
H
l
34
O
O
O
O
H
30
O
31
O
O
HO
k
O
O
Ph
26 X = OH, Y = H
27 X = H, Y = OH
OCOPh
O
e
O
O
24
OCOPh
O
O
23
O
27
OH
14
b
337
Ph H
m
36
Ph H
35
Scheme 3. Reagents, conditions and yields: (a) Li, liq. NH3, THF, 10 min, 75%; (b) PdCl2, CuCl, DMF, H2O, O2, rt, 20 h, 86%; (c) (CH2OH)2,
PTSA, C6H6, reflux, 45 min, 72%; (d) Li, liq. NH3, THF, 15 min, 89% (26:27 3:1); (e) C6H5COCl, py, DMAP, CH2Cl2, rt, 8 h, 95%; (f) 3 N HCl,
THF, 2 h, 87%; (g) piperidine, AcOH, C6H6, reflux, 1 h, 90%; (h) LHMDS, TMSCl, Et3N, THF, 2 h, 70 °C; Pd(OAc)2, CH3CN, rt, 4 h, 80%; (i)
Me2CuLi, Et2O, 1 h, 30 °C; (j) hm, MeOH, 1 h, 65%; (k) hm, MeOH, 2 h, 87%; (l) LHMDS, TMSCl, Et3N, THF, 70 °C, 2 h; Pd(OAc)2, CH3CN,
4 h, 80%; (m) Me2CuLi, Et2O, 30 °C, 1 h, 63%; (n) K2CO3, MeOH, 50 °C, 4 h, 100%.
solanascone 22, mp 168–169.5 °C, in 86% yield, whose
structure was confirmed by single crystal X-ray diffraction analysis (Fig. 1).15 The stereochemistry of the
hydroxy and secondary methyl groups in the ketoalcohol 22 was epimeric to those of the aglycone 8.
For generation of the hydroxy group with correct stereochemistry, reduction of the keto-ketal 14 via single
electron transfer methodology was investigated.12 Reaction of the keto-ketal 14 with lithium in liquid ammonia
and THF, however, furnished exclusively the diquinane
23 in a highly regio- and stereoselective manner, in 75%
Figure 1. ORTEP diagram of the 2a-hydroxy-10-epi-solanascone 22.
yield. Formation of the diquinane 23 can be readily
explained via transfer of an electron to the ketone group
in 14 followed by 5-exo trig cyclisation of the resultant
radical anion.13
In order to prevent the radical cyclisation reaction, it
was decided to carry out the sequence with the bisketal
24 of triketone 25. Consequently, Wacker oxidation11 of
the dione 11 followed by selective ketalisation of the
resultant trione 25 furnished the bisketal 24. Reaction
of the bisketal 24 with lithium in liquid ammonia and
THF furnished a 3:1 epimeric mixture of the alcohols
26 and 27, which were separated by column chromatography on silica gel. The relative stereochemistry of the
major alcohol 26 was established by converting it to
the diketobenzoate 17. The major alcohol 26 was reoxidised to 24 and the sequence was continued with the
minor alcohol 27. Treatment of the alcohol 27 with benzoyl chloride in the presence of a catalytic amount of
DMAP in pyridine furnished the benzoate 28 in 95%
yield, which on treatment with 3 N aqueous hydrochloric
acid furnished the diketobenzoate 29 in 87% yield.
Refluxing a benzene solution of the diketobenzoate 29
with piperidine and acetic acid using a Dean–Stark water
trap furnished the enone 30 in a highly regioselective
manner, in 90% yield. Reaction of the enone 30 with
338
A. Srikrishna, S. S. V. Ramasastry / Tetrahedron Letters 47 (2006) 335–339
Figure 2. ORTEP diagram of the keto-benzoate 36.
LHMDS, trimethylsilyl chloride and triethylamine followed by oxidative desilylation14 of the resultant silyl
dienolate with palladium acetate in dry acetonitrile furnished the cross-conjugated dienone 31 in 80% yield.
Reaction of the dienone 31 with lithium dimethylcuprate
in ether at 30 °C for 1 h furnished the enone 32, which
on photochemical irradiation with a 450 W Hanovia
medium pressure mercury vapor lamp furnished
10-epi-solanascone derivative 33, mp 124–125 °C,15
in 65% yield.
In order to generate the secondary methyl group with
correct stereochemistry, the sequence was altered and
the secondary methyl group was introduced after the
construction of the tetracyclic framework.8 Consequently, irradiation of the enone 30 in methanol with
a 450 W Hanovia medium pressure mercury vapor lamp
for two hours furnished the keto-benzoate 34 in 87%
yield. Treatment of the tetracyclic ketone 34 with
LHMDS, trimethylsilyl chloride and triethylamine followed by reaction of the resultant silyl enol ether with
palladium acetate in acetonitrile furnished the enone
35 in 80% yield. Treatment of the enone 35 with lithium
dimethylcuprate at 30 °C furnished the keto-benzoate
36, mp 168–170 °C, in 63% yield. The stereostructure
of the keto-benzoate 36 was confirmed by X-ray diffraction analysis (Fig. 2).15 Finally, hydrolysis of the benzoate group in 36 furnished the keto-alcohol15 8, the
aglycone of the glycoside 6, in quantitative yield.
In summary, we have accomplished the first total synthesis of the aglycone 8 of the phytoalexin 2b-hydroxysolanascone-b-glucopyranoside 6 isolated from fluecured tobacco leaves, and its 2,10-diepi- and 2a-epimers,
starting from the readily available monoterpene (R)carvone via 3-butenylcarvone.
Acknowledgements
We thank the Council of Scientific and Industrial
Research, New Delhi, for the award of a senior research
fellowship to S.S.V.R.
References and notes
1. Fujimori, T.; Kasuga, R.; Keneko, H.; Sakamura, S.;
Noguchi, M. J. Chem. Soc., Chem. Commun. 1978, 563–
564.
2. Even though different numbering was given to solanascones based on their biogenesis, in the present manuscript
we followed the systematic numbering.
3. Nishikawaji, S.; Fujimori, T.; Matsushima, S.; Kato, K.
Phytochemistry 1983, 22, 1819–1820.
4. Kodama, H.; Fujimori, T.; Kato, K. Agric. Biol. Chem.
1985, 49, 2537–2541.
5. Tazaki, H.; Kodama, H.; Fujimori, T. Agric. Biol. Chem.
1986, 50, 2231–2235.
6. Tazaki, H.; Kodama, H.; Ohnishi, A.; Fujimori, T. Agric.
Biol. Chem. 1989, 53, 3037–3038.
7. Kodama, H.; Fujimori, T.; Tanaka, H.; Kato, K. Agric.
Biol. Chem. 1985, 49, 1527–1528.
8. To the best of our knowledge there is no report on the
synthesis (either racemic or enantioselective) of any of the
hydroxysolanascones. For the enantiospecific synthesis of
the parent solanascone and dehydrosolanascones, see:
Srikrishna, A.; Ramasastry, S. S. V. Tetrahedron Lett.
2005, 46, 7373–7376.
9. (a) Srikrishna, A.; Dethe, D. H. Tetrahedron Lett. 2005,
46, 3381–3383; (b) Srikrishna, A.; Hemamalini, P. Indian
J. Chem. 1990, 29B, 152–153.
10. Smith, J. G. Synthesis 1984, 629–656; Srikrishna, A.;
Ramasastry, S. S. V. Tetrahedron: Asymmetry 2005, 46,
2973–2979.
11. Tsuji, J.; Shimizu, I.; Yamamoto, K. Tetrahedron Lett.
1976, 17, 2975–2976.
12. Mitsunobu inversion of the alcohols 15 and 22 was
attempted under standard conditions; however it was
unsuccessful probably due to the neopentylic nature of the
alcohols.
13. Belotti, D.; Cossy, J.; Pete, J. P.; Portella, C. Tetrahedron
Lett. 1985, 26, 4591–4594.
14. Ito, Y.; Hirao, T.; Saegusa, T. J. Org. Chem. 1978, 43,
1011–1013.
15. Yields refer to isolated and chromatographically pure
compounds. All the compounds exhibited spectral data
(IR, 1H and 13C NMR and mass) consistent with their
structures. Selected spectral data for (1R,2S,4S,5S,7S,
10S,11S)-5,10,11-trimethyl-8-oxotetracyclo[5.3.1.11,4.05,11]
dodecan-2-ol (22): mp: 168–169.5 °C; ½a24
D +162.8 (c 0.7,
CHCl3); IR (thin film): mmax/cm1 3426, 1670; 1H NMR
(400 MHz, CDCl3): d 4.23 (1H, dd, J 10.6 and 5.3 Hz),
2.68 (1H, dd, J 16.2 and 10.0 Hz), 2.62–2.50 (1H, m), 2.41
(1H, dd, J 10.8 and 7.4 Hz), 2.05 (1H, d, J 13.2), 2.10–2.00
(2H, m), 1.94 (1H, dd, J 16.0 and 4.8 Hz), 1.75 (1H, d, J
5.3 Hz, H-4), 1.67 (1H, ddd, J 11.7, 3.9 and 1.8 Hz), 1.43
(3H, s), 1.34 (1H, ddd, J 13.2, 5.1 and 3.6 Hz), 1.20 (1H, d,
J 11.6 Hz), 1.15 (3H, s), 1.00 (3H, d, J 6.9 Hz); 13C NMR
(75 MHz, CDCl3): d 218.3 (C), 73.3 (CH), 54.2 (C), 51.0
(CH), 48.5 (C), 45.6 (CH2), 44.2 (C), 43.2 (CH), 35.3
(CH2), 33.1 (CH2), 32.9 (CH2), 27.3 (CH), 19.2 (CH3),
17.9 (CH3), 17.6 (CH3); mass: 234 (M+, 1%), 190 (50), 175
(9), 164 (11), 137 (68), 121 (44), 120 (100), 105 (44), 91
(28); HRMS: m/z calcd for C15H22O2Na (M+Na):
257.1517; Found: 257.1510. For (1R,2R,4S,5S,7S,
10S,11S)-5,10,11-trimethyl-8-oxotetracyclo[5.3.1.11,4.05,11]
dodec-2-yl benzoate (33): mp: 124–125 °C; ½a25
D +19.1 (c
0.68, CHCl3); IR (neat): mmax/cm1 1714, 1601; 1H NMR
(300 MHz, CDCl3 + CCl4): d 8.01 (2H, d, J 7.2 Hz), 7.56
(1H, t, J 7.2 Hz), 7.44 (2H, t, J 7.2 Hz), 5.22 (1H, d, J
6.6 Hz), 2.80–2.67 (2H, m), 2.60 (1H, dd, J 12.0 and
6.6 Hz), 2.20 (1H, ddd, J 14.7, 6.9 and 2.7 Hz), 2.11 (1H,
dd, J 12.9 and 6.3 Hz), 1.96–1.73 (5H, m), 1.40 (1H, ddd, J
14.4, 4.8 and 2.4 Hz), 1.33 (3H, s), 1.10 (3H, s), 1.17 (3H,
d, J 6.9 Hz); 13C NMR (75 MHz, CDCl3 + CCl4): d 216.1
(C), 166.0 (C), 133.0 (CH), 130.7 (C), 129.6 (2 C, CH),
128.4 (2 C, CH), 76.7 (CH, C-2), 54.4 (C), 50.3 (C), 49.3
(CH), 45.8 (CH2), 44.1 (C), 42.8 (CH), 35.6 (CH2), 33.8
A. Srikrishna, S. S. V. Ramasastry / Tetrahedron Letters 47 (2006) 335–339
(CH2), 32.3 (CH2), 31.5 (CH), 21.6 (CH3), 18.0 (CH3),
17.1 (CH3); Mass: 216 (M+PhCOOH, 8%), 201 (4), 190
(5), 149 (16), 121 (12), 105 (100); HRMS: m/z calcd for
C22H26O3Na (M+Na): 361.1780; Found: 361.1796.
For(1R,2R,4S,5S,7S,10R,11S)-5,10,11-trimethyl-8-oxotetracyclo[5.3.1.11,4.05,11]dodec-2-yl benzoate (36): mp: 168–
1
170 °C; ½a24
D 40.0 (c 0.5, CHCl3); IR (neat): mmax/cm
1714; 1H NMR (400 MHz, CDCl3): d 8.01 (2H, d, J
7.3 Hz), 7.57 (1H, t, J 7.3 Hz), 7.45 (2H, t, J 7.3 Hz), 5.15
(1H, d, J 6.4 Hz), 2.75 (1H, q, J 7.9 Hz), 2.60–2.54 (2H,
m), 2.26 (1H, ddd, J 14.6, 6.3 and 2.7 Hz), 2.20–1.92 (4H,
m), 1.82 (1H, d, J 4.7 Hz), 1.73 (1H, d, J 11.5 Hz), 1.45
(1H, dd, J 14.7 and 4.9 Hz), 1.38 (3H, s), 1.15 (3H, s), 1.05
(3H, s); 13C NMR (100 MHz, CDCl3): d 218.0 (C), 166.0
(C), 133.0 (CH), 130.6 (C), 129.4 (2C, CH), 128.4 (2C,
CH), 74.6 (CH), 53.4 (C), 49.1 (C), 48.2 (CH), 46.4 (CH2),
45.2 (C), 43.3 (CH, C-4), 38.4 (CH2), 36.2 (CH2), 34.4
(CH2), 34.1 (CH), 19.4 (CH3), 18.0 (CH3), 17.8 (CH3);
mass: 216 (M+PhCOOH, 6%), 204 (5), 190 (3), 135 (7),
121 (12), 120 (20), 105 (100), 91 (10); HRMS: m/z calcd for
C22H26O3Na (M+Na): 361.1780; Found: 361.1779; Anal.
Calcd for C22H26O3 C, 78.07; H, 7.74. Found: C, 77.80; H,
7.72. For (1R,2R,4S,5S,7S,10R,11S)-5,10,11-trimethyl-8oxotetracyclo[5.3.1.11,4.05,11]dodecan-2-ol (8): ½a25
D +21.8
(c 0.64, CHCl3); IR (neat): mmax/cm1 3465, 1704; 1H
NMR (300 MHz, CDCl3): d 4.03 (1H, d, J 6.6 Hz), 2.65–
2.50 (2H, m), 2.50 (1H, dd, J 11.7 and 5.7 Hz), 2.20–2.05
(2H, m), 2.03 (1H, ddd, J 14.1, 6.6 and 2.7 Hz), 1.91 (1H,
t, J 12.3 Hz), 1.82 (1H, br d, J 12.3 Hz), 1.75 (1H, d, J
4.5 Hz), 1.52 (1H, d, J 11.7 Hz), 1.35–1.20 (2H, m), 1.29
(3H, d, J 6.6 Hz), 1.26 (3H, s), 0.98 (3H, s); 13C NMR
(100 MHz, CDCl3): d 218.5 (C), 70.0 (CH), 54.2 (C), 49.0
(C), 48.2 (CH), 46.6 (CH2), 45.0 (C), 43.1 (CH), 38.1
(CH2), 36.8 (CH2), 34.5 (CH2), 33.7 (CH), 19.6 (CH3),
18.0 (CH3), 17.5 (CH3); Mass: 190 (M+CH3CHO, 14%),
164 (10), 147 (6), 137 (100), 135 (10), 121 (25), 120 (53),
105 (30), 91 (23); HRMS: m/z Calcd for C15H22O2Na
339
(M+Na): 257.1517; Found: 257.1509. Crystal data for the
alcohol 22: X-ray data were collected at 293 K on a
SMART CCD-BRUKER diffractometer with graphitemonochromated MoKa radiation (k = 0.71073 Å). The
structure was solved by direct methods (SIR92). Refinement was by full-matrix least-squares procedures on F2
using SHELXL-97. The non-hydrogen atoms were refined
anisotropically whereas hydrogen atoms were refined
isotropically. C15H22O2; MW = 234.3; colourless crystal;
crystal system: monoclinic; space group P2(1); cell parameters, a = 7.719(13) Å, b = 8.429(14) Å, c = 9.954(17) Å;
V = 647.62(2) Å3, Z = 2, Dc = 1.202 g cm3, F(000) =
256, l = 0.078 mm1. Total number of l.s. parameters = 161, R1 = 0.064 for 1697 Fo > 4r(Fo) and 0.092
for all 2255 data. wR2 = 0.134, GOF = 1.076, restrained
GOF = 1.076 for all data. An ORTEP diagram of 22 is
depicted in Figure 1. Crystallographic data has been
deposited with the Cambridge Crystallographic Data
Centre (CCDC 284283). Crystal data for the keto-benzoate 36: X-ray data were collected at 293 K on a SMART
CCD-BRUKER diffractometer with graphite-monochromated MoKa radiation (k = 0.71073 Å). The structure
was solved by direct methods (SIR92). Refinement was
done by full-matrix least-squares procedures on F2 using
SHELXL-97. The non-hydrogen atoms were refined
anisotropically whereas hydrogen atoms were refined
isotropically. C22H26O3; MW = 338.4; colourless crystal;
crystal system: monoclinic; space group C2; cell parameters, a = 20.595(57) Å, b = 7.798(21) Å, c = 11.834(33) Å;
V = 1884.55(13) Å3, Z = 4, Dc = 1.19 g cm3, F(000) =
727.9, l = 0.078 mm1. Total number of l.s. parameters = 229, R1 = 0.066 for 2768 Fo > 4r(Fo) and 0.080
for all 3282 data. wR2 = 0.138, GOF = 1.221, restrained
GOF = 1.221 for all data. An ORTEP diagram of 36 is
depicted in Figure 2. Crystallographic data has been
deposited with the Cambridge Crystallographic Data
Centre (CCDC 284284).